A patient presents with diarrhea and dehydration. A fecal smear stained by Gram's method revealed Gram-negative, comma-shaped bacteria. What is the causative agent?

Correct Answer: A

Rationale: The correct answer is A: Vibrio cholerae. Vibrio cholerae is the causative agent of cholera, which presents with severe watery diarrhea leading to dehydration. The characteristic comma-shaped (curved rod) appearance of Gram-negative bacteria is typical of Vibrio cholerae. This bacterium produces the cholera toxin, leading to the excessive secretion of fluid into the intestines. Salmonella typhi causes typhoid fever with symptoms like sustained fever, not watery diarrhea. Shigella dysenteriae causes bloody diarrhea and abdominal cramps. Escherichia coli can cause various types of infections, but typically not severe watery diarrhea like cholera.

Correct Answer: B

Rationale: The correct answer is B: halophiles. Halophiles are bacteria that thrive in high salt environments. They have adapted to survive and grow in areas with high salt concentrations. This preference for high salt levels is what distinguishes halophiles from other types of bacteria. A: Calciphiles are bacteria that prefer high levels of calcium. C: Osmophiles are bacteria that thrive in environments with high sugar concentrations. D: Mesophiles are bacteria that prefer moderate temperature ranges for growth. In summary, the correct term for bacteria that prefer high levels of salt in their growing environment is halophiles, making choices A, C, and D incorrect in this context.

Correct Answer: A

Rationale: The correct answer is A: Type IV hypersensitivity reaction. This type of reaction is characterized by a delayed response involving T cells. In this case, the appearance of a papule after 48 hours indicates a delayed hypersensitivity reaction, which is typical of a Type IV reaction. The other choices are incorrect because: B: Arthus phenomenon is a localized immune complex-mediated reaction, not seen in tuberculin tests. C: Seroreaction typically involves antibodies reacting with soluble antigens, not seen in this scenario. D: Type II hypersensitivity reactions involve antibodies targeting specific cells or tissues, which is not the mechanism at play in this case.

Correct Answer: A

Rationale: The most probable diagnosis is Leptospirosis. The symptoms described align with the classic presentation of Leptospirosis, such as fever, muscle pain, headache, jaundice, and hemorrhages. The initial symptoms of chills, high fever, and muscle pain followed by jaundice and hemorrhages are characteristic of Leptospirosis. The presence of dark urine and low diuresis also point towards kidney involvement, which is common in Leptospirosis due to renal failure. Additionally, the patient's history of potential exposure to contaminated water or soil supports the diagnosis, as Leptospirosis is commonly transmitted through contact with infected animal urine. Summary of other choices: - Typhoid fever typically presents with sustained fever, abdominal pain, and constipation, not matching the symptoms described. - Virus A hepatitis usually presents with jaundice, but other symptoms such as muscle pain and hemorrhages are not typical. - Sepsis is a systemic response

Correct Answer: A

Rationale: 1. Vaccination introduces antigens to stimulate immune response. 2. T and B cells are activated to produce memory cells for long-lasting protection. 3. Active immunity develops over time post-vaccination. 4. Choice A is correct as it accurately describes the process and outcomes. 5. Choice B is incorrect as it contradicts the process of active immunity. 6. Choice C is incorrect as the process of active immunity is consistent regardless of the situation. 7. Therefore, the correct answer is A as it aligns with the mechanism and characteristics of artificial active immunity.

Correct Answer: D

Rationale: The correct answer is D: Multiplies by binary fission. Bacterial cells reproduce through binary fission, where a single cell divides into two identical daughter cells. This process is essential for bacterial growth and multiplication. A: The oxidative phosphorylation does not take place in the mitochondria of bacterial cells but in the cell membrane. B: Capsules are not organelles but outer protective layers found in some bacterial cells. C: Bacterial cells contain both DNA and RNA, essential for their genetic information and protein synthesis.

Correct Answer: D

Rationale: The correct answer is D. Cytoplasmic inclusions in bacteria refer to substances like granules. These granules can be excess products of metabolism or reserve substances stored for future use. Therefore, all of the choices are correct as cytoplasmic inclusions can be any of these substances. A is correct as it directly refers to cytoplasmic inclusions. B is correct as some granules can be excess metabolic products. C is correct as certain granules can serve as reserve substances. Therefore, the correct answer is D, as it encompasses all the possible types of substances found as cytoplasmic inclusions in bacteria.

Correct Answer: A

Rationale: Step 1: Oval, round, elongated chains of gemmating cells indicate yeast-like budding cells seen in Candida species. Step 2: Candidosis is caused by Candida species, which is commonly found in the oral cavity and can cause infections on the tongue. Step 3: Candidosis presents as white patches or plaques on the tongue. Step 4: Therefore, the correct answer is A: Candidosis. Summary: B: Actinomycosis is caused by Actinomyces species, which are filamentous bacteria, not oval budding cells. C: Diphtheria is caused by Corynebacterium diphtheriae, which appears as gram-positive rods in chains, not oval budding cells. D: Staphylococcal infections are caused by Staphylococcus species, which appear as clusters of cocci, not oval budding cells.

Correct Answer: C

Rationale: The correct answer is C: Inhibits protein synthesis. Exotoxin of C. Diphtheriae acts by inhibiting protein synthesis in host cells. This disrupts cellular functions and leads to tissue damage. Choice A is incorrect because acetylcholine release is not affected. Choice B is incorrect as it does not involve neurotransmitters. Choice D is incorrect as the exotoxin does have a specific mechanism.